Extended Forecast Discussion
NWS Weather Prediction Center College Park MD
212 AM EDT Sun Oct 02 2022
Valid 12Z Wed Oct 05 2022 - 12Z Sun Oct 09 2022
A wavy pattern should be in place by the start of the medium range
period on Wednesday, with a compact upper low shifting off the
Mid-Atlantic coast and a shortwave moving into the Upper Midwest.
By Thursday-Friday, energy diving southward across Canada
combining with the latter shortwave will act to amplify upper
troughing across the East while ridging builds over the West, with
this pattern remaining generally stagnant into next weekend.
Relatively quiet weather conditions are expected across the CONUS
besides some monsoonal moisture and weak energy over the Southwest
leading to showers and storms and perhaps extending into portions
of the Plains. The large-scale trough should push a potent cold
front across the central and eastern U.S., with potential for some
rain particularly in the Upper Great Lakes and considerably cooler
temperatures behind the front.
...Guidance Evaluation/Predictability Assessment...
Model guidance remains in good enough agreement through Friday to
warrant a general model blend. By next weekend though, models
begin to diverge some regarding details and timing of individual
pieces of energy into the larger scale Eastern U.S. trough. There
isn't a lot of run to run consistency and these systems are small
scale that it's tough to choose one solution or pattern evolution
over another. The 01/18Z GFS and 01/12Z CMC were a little more
consistent with each other over the ECMWF which showed a bit more
amplification. Preferred a solution weighted more towards the
GFS/CMC and ensemble means for 6 into 7. This also worked well out
west where individual ensemble members show quite a bit of spread
regarding energy rounding the top of the ridge into the Rockies
and how much influence this might have on ridge breakdown. The QPF
forecast was based largely on the 02/01Z National Blend of Models
but with a wider footprint for light amounts added across much of
the country as this under forecast of low amounts from the NBM is
a known bias.
Rainfall and gusty winds associated with a compact upper low
exiting the Mid-Atlantic coast on Wednesday should be offshore by
the start of the medium range period, with only some lingering
showers along coastal locations expected. Meanwhile, monsoonal
moisture into the Southwest will continue to drive some diurnal
showers and thunderstorms, with locally heavy rainfall possible.
Rainfall intensity should wane after Wednesday, but showers could
linger through the rest of the week across the Four Corners
states. To the north, a cold front shifting from the Northern
Plains to the Upper Midwest and Great Lakes should result in
scattered showers as the front moves through.
Temperatures out West will trend much warmer by Wednesday
underneath a blocky upper ridge with daytime highs over the
Northwest 10 to 15 degrees above normal through next weekend.
Despite the anomalies, the resulting temperatures peaking in the
70s and 80s (90s for parts of California) are unlikely to create
any heat related hazards. Canadian high pressure spilling into the
north-central U.S. and expanding eastward behind the cold front
will result in much below normal temperatures shifting from the
northern Plains into the Midwest and the Northeast
Thursday-Sunday. Daytime highs in some locations could be 15 to 20
degrees below average with overnight temperatures dropping into
the 30s for many, and even 20s for far northern areas of North
Dakota/Minnesota particularly Friday morning.
Additional 3-7 Day Hazard information can be found on the WPC
medium range hazards outlook chart at:
WPC medium range 500mb heights, surface systems, weather grids,
quantitative precipitation, experimental excessive rainfall
outlook, winter weather outlook probabilities and heat indices are